


Lesson learned

by LazySintastic13 (EmeraldWriter)



Category: Undertale (Video Game)
Genre: Cloaca, Dubious Consent, Ecto-Body (Undertale), Ecto-Genitalia (Undertale), Ecto-Penis (Undertale), Impregnation, M/M, Referencing Red Scales, Scents & Smells, Underfell Sans (Undertale), Underfell papyrus mentioned, magic binding, mermaid au
Language: English
Status: Completed
Published: 2021-03-15
Updated: 2021-03-15
Packaged: 2021-03-23 16:22:09
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 876
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/30058236
Author URL: https://archiveofourown.org/users/EmeraldWriter/pseuds/LazySintastic13
Summary: Red’s been annoying Sans for the past couple of days.And Sans has had enough.
Relationships: Sans/Sans (Undertale), Undertale Sans/Underfell Sans - Relationship
Comments: 4
Kudos: 54





	Lesson learned

**Author's Note:**

  * For [Mus_reads](https://archiveofourown.org/users/Mus_reads/gifts).



“Urgh.” Slammed against the ground by the other mer, Sans gnashed his teeth whilst glaring at the cocky grin on top of him, sharp teeth and menacing. Wrists pinned down, they were by the edge of the pool, and the so-called ‘Boss’ had gone to some errand. Apparently. 

“Heh, dun be scared sweetheart, I’ll show you the ropes. Swear I’ll be gentle.” A red ectocock springs out, shamelessly rutting against Sans’ tail, urging him to make a cloaca. “Come on, you want this too. I can smell it on ya.” 

A cloyingly sweet scent … Red’s been smelling it everywhere, and Sans could too. 

Except that … it hadn’t been coming from Sans.

With a click of his tongue, the blue merskeleton flipped their positions, causing Red to yelp in surprise. He’s about had it enough with this stupid brat. “That’s  _ you.” _

“What?” Red has no idea what the other fish was talking about. The scent was him? That can’t be right. If he smelled like this before, then Boss would’ve complained about it. “You high or somethin? It’s obviously you.” Must be the medicine or something. Messing with Sans’ head. 

But how could Red know more about his own kind than Sans? 

The blue merskeleton huffed, unavoidably taking in more whiffs of the sweetness, thickening in the air. 

_ Cherries _ .

Coaxing and inviting. 

It’s been days with Red trying to make advances towards him with it, increasing in its potency with each passing day. 

He’d been able to hold back, but his patience had run thin. 

“You’re the one who’s been begging for it.  _ Seducing _ me.” 

Sans used his magic to keep Red’s arms stuck to the floor; because he’d be damned if he doesn’t teach him a lesson himself. With his hands free to roam, he caressed unmarred bones, surprisingly. A contrast to his wounds, but it showed a truth. Red was a sheltered merskeleton. 

“Since you don’t know, then I’ll just show you.” 

Suddenly, a citrusy tangy scent intertwined with cherries—lemon—among spices that melded soon after. Beginning to dominate the cherries, and causing the red merskeleton to feel lightheaded. 

“Wh-What?” His body reacted on its own. Dissipating his cock, and summoning a cloaca in its stead. 

“Heh. That’s better.” Without waiting, Sans plunged two fingers deeply into the hole, groaning at the tightness as Red outright screamed and arching; wishing to move away but couldn’t. 

“Take it out! Take it—hhck! Aahh! Nggh!!” His red tail flapped to get the other off, but another binding magic had his tail pinned to the side pool tile. Rendering him completely immobile. 

Sans pumped in and out to get the other leak out enough slick akin to drool, relishing in the small keens from that annoying mouth whenever he grazed against sensitive spots. It wouldn’t be enough, barely stretched, but how could it be a punishment otherwise? 

Red would learn today. 

Sans summoned his cock as he took his fingers out. A bulbous head with a thick shaft, sliding against the small twitching hole. 

“Wai—That’s not—”

“Shut up.” 

Red’s head tilted back, his chest arching up as his eye sockets widened and eye lights shrunk, with his mouth opened in a silent scream. 

Sans thrusted into the hot cavern, hilting to the base, and gripped onto Red’s hips, as quivering walls clenched down on him. And he didn’t wait for the other to adjust either. 

Pulling back just as the head would get caught, and slamming back into the depths in a punishing pace that only became faster as more of Red’s slick spilled and aided in the movement. 

“Heh, see. It’s you who wanted this. Look how far I’m going.” 

Each slam caused a slight protrusion on Red’s belly, and each time, a wave of pleasure would come crashing down on Red’s core, electrifying and tingling. An addictingly new sensation that has him wanting, and needing for more. 

Through hot tears that began spilling down Red’s cheeks, he looked at the bump that’d appear when Sans pushed in. Hitting something … important. 

Though confused, his instincts told him that it would be bad. And yet, the myriad of pleasure has his will dwindling. His throat was becoming parched from all his crying. “D-Don—” 

“I can easily reach your womb. You’re not even resisting.” 

_ W-Womb? _ He tightened at the thought, whimpering, despite not knowing what was going on. What was happening to him. His body was just reacting,  _ accepting _ . It wanted what Sans was giving him. 

But … “B-Boss won’t—hcck—He won’t–Aaah!” 

“Won’t what? Want you full and round with my clutch? Heh, wonder what the look on his face be when he comes home and it’s already too late.”

“S-Sansh—!!!” Red keened and shamelessly climaxed in a pitiful cry. It forced Sans to come unbiddenly from the sudden constriction, painting the walls and filling up the womb with a thick load; fertilizing the eggs. 

The bulge on Red’s stomach grew noticeably, before it stopped. And merskeleton was left revelling in the feeling of fullness and warmth. 

Sans looked down at the dazed skeleton then down to the translucent blue he could see in Red’s ectobody that was still trembling and twitching in the aftermath. 

Oh there will be quite a surprise when Boss comes back. 

**Author's Note:**

> Hope you enjoy and I did it some justice X’D


End file.
